Gene Expression

• What is a gene mutation?

  A change in the nucleotide sequence of a gene
• What is a substitution mutation?

  When one nucleotide replaces another nucleotide - Generally not harmful due to degenerate UNLESS codes for a premature stop codon - Changes the tertiary structure of the protein

  results in a non functional proteins
• What is a deletion mutation?


  When one nucleotide is removed causing a frameshift mutation

  This can affect every other codon
• What is an addition mutation?


  When a base is added
• What is a duplication mutation?

  When one or more bases are repeated
• What is an inversion mutation?

  A codon sequence is inversed
• What is a translocation mutation?


  When a sequence of bases are removed from one chromosome and are added to a different chromosome
• Mutagenic agent examples


  UV radiation, chemicals in cigarette
• What are mutagens that cause cancer called?

  Carcinogens
• What are totipotent cells?

  Cells that can develop into any other cell in the body
• Where are totipotent cells found?

  Embryonic cells
• What does 'switched off' mean in terms of genes?

  Cannot make protein - Phenotype unable to be expressed
• Why do cells lose their totipotency?


  Certain genes become switched off

  Irreversibly specialised due to different proteins being able to be expressed
• What does 'switched on' mean in terms of genes?

  Can make protein - phenotype expressed
• What are pluripotent cells?

  -Embryonic stem cells

  -Can produce almost all cell types

  -Can divide unlimitedly

  -Can be used in treating disorders
• What are multipotent cells?

  -Adult stem cells

  -Able to produce some specialised cells
• What are unipotent cells?

  -Adult stem cells

  -Can only produce one cell type
• What are iPS cells?

  Induced pluripotent stem cells
• What are the pros of using embryonic stem cells to treat human disorders?

  Regenerative medicine - stem cell transplants to treat leukaemia

  Explorative research - Understand the function of genes in making stem cells
• What are the cons of using embryonic stem cells to treat human disorders?

  Ethical issues - Stem cells taken from embryos

  Could be rejected by the patient
• What are transcription factors? Give an example

  Receptor molecules that aid transcription
• How does oestrogen act as a transcription factor to switch a gene on?

  -Diffuses directly through the phospholipid bilayer

  -Binds to the complementary receptor on a transcription factor

  -Transcription factor now activated

  -Travels through nuclear pore

  -Binds to DNA and stimulates transcription of specific gene
• How does small-interfering RNA (siRNA) switch genes off?

  Breaks down mRNA before it can be translated, so gene is switched off
• Describe the process where siRNA breaks RNA

  -Double stranded RNA is broken up by an enzyme into siRNA

  -One of the two strands of siRNA combines with an enzyme

  -The siRNA strand pairs with complementary bases on mRNA

  -The enzyme cuts the mRNA into smaller sections
• What is epigenetics?


  How the environment can subtly influence the expression of genes without changing the base sequence of DNA
• What is heterochromatin?


  Genes that are turned off due to limited space between histones therefore transcription factors cannot interact with DNA
• What is euchromatin?


  Genes that are turned on due to space between histories allowing for interaction between transcription factors and DNA
• What is the effect of acetylation on gene expression?


  -Addition of an acetyl group (COCH3) from acetyl CoA to histones

  -Increased space between histones

  -Accessible to transcription factors

  - Euchromatin = gene turned on
• What is the effect of methylation on gene expression?

  - Addition of methyl group (CH3) to DNA

  - Decreased space between histones

  - Not accessible to transcription factors

  - Heterochromatin = gene turned on off
• What is cancer?


  A growth disorder caused by the uncontrolled division of cells
• How do benign and malignant tumours differ in terms of growth?

  Benign tumours grow slowly, malignant tumours grow quickly
• How do benign and malignant tumours differ in terms of appearance?

  Benign tumours appear normally, malignant tumours appear darker due to their nucleus contain more DNA
• How do benign and malignant tumours differ in terms of treatment?

  Benign can be treated more easily by surgery, malignant requires aggressive/cancer/repeated treatment
• What does a proto-oncogene control?

  Stimulates cell division
• What does a tumour suppressor gene control?

  Slows cell division
• What does happens when a proto-oncogene mutates?


  Gene becomes oncogene - rate of cell division increases
• What happens when a tumour suppressorgene mutates?

  Tumour suppressor gene become inactivated - rate of cell division increases
• What do cancer cells in the breast contain?

  Oestrogen receptors
• Why are post-menopausal women more likely to develop breast cancer?

  Higher levels of oestrogen
• How can breast cancer be prevented?

  Mastectomies - removal of breast tissue with oestrogen receptors